More Cranberries, Fewer Urine Infections

Sept. 30, 2004 -- You may have heard that cranberry juice helps prevent urinary tract infections. Now, research shows that the amount of cranberry juice you drink may determine how much protection you get.

Urinary tract infections are common infections that affect millions of people annually. Most are caused by a common bacteria called E coli., which lives in the intestine and requires antibiotic treatment.

There's been evidence that cranberry juice and other products can prevent and even treat simple urine infections, and now researchers may have an indication as to how much is needed to better fight bacteria and stop it from infecting the bladder.

Drinking 8 ounces of cranberry juice more than doubled the protection against infection compared with drinking 4 ounces, according to a recent study by Kalpana Gupta, MD, MPH, of Yale University, and colleagues from the University of Washington and Rutgers University.

Urinary tract infections (UTIs) can occur anywhere in the urinary tract, including the kidneys, bladder, and urethra. Women are at higher risk than men because their shorter urethra and hormones make them more susceptible to urine infections. Symptoms include a frequent need to urinate and pain or burning during urination.

Study Results

In the study, three volunteers provided urine samples, drank 4- or 8-ounce servings of cranberry juice cocktail, and then provided more urine samples four to six hours after drinking the two different serving sizes of cranberry juice.

The researchers combined each of the urine samples with human bladder cells and E. coli bacteria. Then, they measured the amount of bacteria that latched on to the bladder cells. E coli bacteria must anchor itself to the bladder in order to cause an infection.

In the women who drank 8 ounces of cranberry juice, the protective effect against infection was more than twice as strong compared with women who drank 4 ounces of cranberry juice.

Credit likely goes to a specific type of tannin found only in cranberries and blueberries.

The tannin interferes with little projections on the E. coli bacteria, preventing them from sticking to bladder walls and causing infection, according to a news release from the Infectious Diseases Society of America (IDSA).

More studies are needed to determine optimal dose levels. The percentage of cranberry juice in a drink may also be important. The study used 27% cranberry juice, according to the IDSA news release.